The overall objective of this project is to determine the mechanisms required for effective vaccination against respiratory pathogens. Previous experiments have demonstrated that intranasal treatment of mice with vaccine and exogenous IL-12 as adjuvant enhances systemic and mucosal antibody responses, and induces protection against viral and bacterial respiratory infections. Further results have indicated that the observed protection is dependent upon the augmented humoral immune response induced by IL-12. Studies in this proposal are now designed to determine how intranasal IL-12 enhances B cell activity in the lung and to investigate the importance of mucosal versus systemic antibody in pulmonary defense. The hypothesis is that IL-12 stimulates local antibody production, primarily IgA production, and this is responsible for initial defense against infection in the lung. IL-12 may also act synergistically with vaccines/infectious agents to induce a degree of inflammation that allows protective IgG antibody to transudate from the bloodstream and provide a back-up mechanism to ensure survival of the host. To test these concepts, B cell subset activation and recruitment into the lung will be assessed after intranasal vaccination [unreadable] IL-12. The contributions of T and NK cells, and the cytokines produced by these cells, to enhanced pulmonary B cell activity will be determined using gene deficient animals and antibody depletion/neutralization. The ability of IL-12 to induce localized antibody secreting cells of defined isotype in the lung as well as organized pulmonary lymphoid tissue will be assessed by a combination of ELISPOT and immunohistochemical analyses. Finally, the relative importance of IgA versus IgG for protection against bacterial and viral infection in the lung will be examined using the backpack model with hybridomas of defined antigen specificity and isotype, IgA and polymeric Ig receptor gene deficient mice, and passive transfer of antisera specifically depleted of IgA or IgG. These latter experiments will be performed to examine the potential role of IL-12 in promoting transudation of IgG antibody into the lung. The immediate goal of the study is to determine how a mucosal adjuvant such as IL-12 can enhance lung humoral immunity and protection against infectious microbes. The ultimate goal is to exploit the information obtained in order to understand the requirements for induction of protective pulmonary immunity and to design effective mucosal vaccine adjuvants for use in humans.